Two days isn't nearly enough time to get to grips with the current Liverpool Biennial, which opens on Saturday.

I hurried through the John Moores Painting Prize exhibition, now in its 50th year. Very little rubbed off on me. Lost in the exhibition City States, which takes us from Birmingham to Gdansk, from Greenland to Taipei, and occupies a vast acreage of Liverpool's former postal sorting office, I could have been anywhere. Here I spent about half an hour circumnavigating a humongous inflatable black pillow, wedged between floor and ceiling, by a collective from Vilnius. The bloated black form might signify the big sleep.

Around a corner are versions of Morris Louis's 1960's drip-and-pour paintings, executed, inexplicably, by North Korean weavers. Why, you ask. The answer is very long indeed.

Every few hours, I slipped down to the waterfront, to check if Anthony McCall's much anticipated column of cloud had yet ascended across the Mersey. Wind and weather and technical glitches have meant that this, the most spectacular of the biennial's works, has yet to take off. Of such mysteries and expectations biennials are made, from Liverpool to Sydney.

Since its inception in 1999, the Liverpool Biennial has itself struggled to take off. Under the new artistic directorship of Sally Tallant, it is trying to refocus. The overall theme, hospitality, is more complex than it sounds, though whether it helps us cross and recross the city in search of its roster of 242 artists in 27 locations, is moot.

Better to sit in a room and think. But not perhaps in Finnish artist Markus Kåhre's fake hotel suite, on the 1st floor of the Monro pub. Everything, from the table lamps to the windows, walls and doors, is a perfect simulacrum, fabricated by the artist. We take it all as real, until we look in the mirrors on the wall, which reflect everything except ourselves. This is disturbing and uncanny, unless you happen to be a vampire or a ghost. Even the daylight is fake.

Kåhre's work is perfectly in tune with the title of the biennial's main exhibition, The Unexpected Guest. In art, we are used to expecting the unexpected, though genuine surprise is rare. Biennial after biennial, the same fashionable names with their familiar stratagems appear. Here comes Dora Garcia, who's always everywhere, there goes Argentinian Jorge Macchi, who "questions our ability to locate ourselves in space", by way of bent iron bars, which intend to simulate the effects of refraction in water. It doesn't work. I much prefer the games room set up by Pedro Reyes at FACT. Somehow, I ended up playing a sexed-up version of snakes and ladders with the Mexican cultural attaché, while small children milled about, whacking each other in a pillow fight.

Sometimes I felt less a guest, more an ingrate, especially as I queued to get into the non-existent nightclub behind Elmgreen and Dragset's freestanding VIP door in the Liverpool ONE shopping precinct. A genial but unmovable doorman tells anyone who asks that they're not on the guestlist.

There are plenty of such lighthearted works here, from the multi-coloured plastic pigeons roosting at the entrance to the Walker Art Gallery (a work that rips-off Maurizio Cattelan's stuffed pigeons that have been in at least two Venice Biennales), to Superflex's Liverpool To Let, a bunting of estate agents' signage, which festoons part of the enormous ground floor space of the Cunard Building, which few artists occupy with any real presence.

Althea Thauberger's video staging of Peter Weiss's 1963 play Marat/Sade, and Sylvie Blocher's video reworkings of speeches by the likes of Angela Davis and Karl Marx, had a real spring and surprise. Marx has never sounded so good as declaimed by a semi-clothed Russian punk rapper.

We are less guests than voyeurs to Japanese photographer Kohei Yoshiyuki's famous but rarely seen The Park, at the Open Eye Gallery. These 1970s images of public sex in a Tokyo park, at night, are more funny than salacious, and shown in a blacked-out room. You search for the images with a torch, and become one with the furtive spectators spying on all the goings-on.

People like to watch, and others like to be watched, and some like to listen. Doug Aitken's The Source, in a building especially designed by David Adjaye, presents a series of interviews with major creative figures about the sources of their creativity. The sound levels are too low and the videos are screened simultaneously about the circular space. It is almost impossible to concentrate on William Eggleston's ruminative mumble, or to focus on Mike Kelley in probably his last interview before his suicide earlier this year. The interviews are great, but Aiken has turned them into a sort of cocktail party babble.

The best work in the biennial is undoubtedly John Akomfrah's The Unfinished Conversation, a three-screen video based on the life, work and talk of the incomparable Jamaican-born thinker Stuart Hall, at the Bluecoat Gallery. Much more than biopic, Akomfrah juxtaposes archive news footage, readings of William Blake, Dickens and Virginia Woolf and most of all Hall's own voice, to describe the world's tumbling. Hall's thoughts about identity, immigration and selfhood, evolve through a roar of telling images. Akomfrah's film, like the essence of Hall's work, is about the conundrum of being in the world, and is as unexpected as it is brilliant.